4/0 LÉPIDOPTÉROLOGIE COMPARÉE 



We have thus extracted a pure line of S S individuals breeding 

 true. As, however, it was assumed that the new form was the 

 stronger, it is clear that it would tend to increase in numbers, 

 and, just as plainly, we can see that the type form would diminish 

 in individuals. Next, one of two things would happen; either 

 the parent form would be totally " swamped " and vanish, 

 leaving us with the new form in its place, or both would continue, 

 with the type form retiring to localities in which the strain of 

 combat with superior forms was not felt, there to continue as a 

 rare form or species. Such an occurrence as the former, we see 

 takmg place before our eyes in the North of England, in the 

 graduai supplanting of Amphidasis betularia by its aberrant 

 form Doubledayaria, for, already, in the country of Durham, no 

 trace of the type form is to be found. An example of the latter 

 state of affairs is seen in the trio of species Larentia autumnalis, 

 Lar. sordidata and Lar. ruberata. The two former have both 

 been evolved from the last by showing strength and adaptability, 

 in providing for lengthened larval existence, during an epoch of 

 constantly diminishing periods of summer heat. The first does 

 it by the robustness of the embryo m the egg, for it hybernates 

 in the egg state. The other succeeds by the power it has acquired 

 of continuing as a spun up larva, in the depths of winter, and 

 then successfully pupating. That Lar. ruberata is the older form 

 is proved by its rarity, and the great discontinuity, combined with 

 the wide area of its distribution. To return to the species we 

 are immediately concerned with. I see in the Lycia-Pœcilopsis 

 group (in the main) the stronger line and in /. zonaria, I. alpina 

 and in the other Ithysiœ, isolated and weaker forms unable to 

 cope under similar conditions, and in like localities, with the 

 others. They have therefore taken to mountainous and seacoast 

 localities just as many plants, which have failed in the battle 

 of life with their more robust neighbours, have donc. There, they 

 have more or less adapted or specialised themselves in ail ways 

 against the attacks of enemies. 



Now, granted that specialised forms have been evolved, and 



